9709 P32 - Jun 2016 - Q5
42
(i) Prove the identity \(\cos 4\theta - 4\cos 2\theta \equiv 8\sin^4\theta - 3\).
(ii) Hence solve the equation \(\cos 4\theta = 4\cos 2\theta + 3\), for \(0^\circ \leq \theta \leq 360^\circ\).
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